1. Field of the Invention
The present invention relates to a substrate processing method of improving the surface condition of a resist film formed in a substrate, such as a semiconductor wafer and a substrate processing system for carrying out the substrate processing method.
2. Description of the Related Art
Usually, a photolithographic process among those for fabricating a semiconductor device includes, a resist film forming process for forming a resist film on a base film formed on, for example, a semiconductor wafer (hereinafter, referred to simply as “wafer”) by applying a resist solution to the wafer, an exposure process for exposing the resist film through a mask provided with a circuit pattern to light to form a latent circuit pattern in the resist film, a developing process for processing the exposed resist film by a developer to form a resist pattern, and an etching process for etching the base film formed on the wafer by using the resist pattern as a mask.
A plurality of vertically arranged horizontal ridges and furrows are formed in the side surfaces of a resist pattern R formed by the developing process due to the wave characteristic of the light used for irradiating the surface of the wafer by the exposure process as shown in FIG. 12. For example, the wavelengths of KrF light and ArF light are 248 nm and 193 nm. Those ridges and furrows are LWR lines (line width roughness lines) and LER lines (line edge roughness lines). In a resist pattern R provided with holes H, round ridges and furrows are formed in the side surfaces of the holes H due to the wave characteristic of light used for irradiating the surface of the wafer by the exposure process. When the resist pattern having surfaces roughened by the ridges and furrows are used for etching the base layer by the etching process, ridges and furrows corresponding to those of the resist pattern R are formed in the base film. Consequently, a precise circuit pattern cannot be formed and hence a semiconductor device of a desired quality cannot be produced.
The inventors of the present invention previously proposed a smoothing method (smoothing process) to improve the surface quality of a circuit pattern by smoothing LWR lines and LER lines in JP-A 2005-19969 (Claims and FIGS. 4, 5 and 16). This previously proposed smoothing method dissolves the surfaces of a resist pattern partly in an atmosphere of a solvent for dissolving the resist. Since an ArF resist dissolves in the organic solvent at a low solubility, the resist film is irradiated with ultraviolet light prior to the smoothing process to decompose a dissolution inhibiting protective group, such as a lactone group.
The technique mentioned in JP-A 2005-19969 carries out an ultraviolet-light irradiation process for irradiating the resist pattern with ultraviolet light and a smoothing process for exposing the resist pattern to an atmosphere of a solvent vapor individually by separate devices. Therefore, the time between the ultraviolet-light irradiation process and the smoothing process is not constant and there is the possibility that processing accuracy is not constant. When an ultraviolet-light irradiation device and a smoothing device are used individually, there is a time interval between the ultraviolet-light irradiation process and the smoothing process. Since the smoothing process uses an atmosphere of solvent vapor, it is possible that the solvent absorbed by the resist pattern diffuses through the substrate into and outside the device.